Environmental toxicity has both direct and indirect impact on human health. Genomics, the global genetic analysis of organisms, is an ideal way to assess the potential impact of chemicals on ecosystems and the environment, as genomic methods simultaneously report both specific and holistic assessments of biological systems. To date, however, genomics infrastructures have not been developed for any of the commonly used and accepted ecotox/environmental monitoring organisms. In this Phase I proposal, we will test the feasibility of developing and using microarrays for the fathead minnow Pimephales promela, one of the standard aquatic toxicity assessment organisms. Specifically, we will construct a pilot array for Pimephales. In developing this Pimephales pilot array, we will test the feasibility of 1) developing reasonably comprehensive arrays, 2) identifying toxic chemicals based on their expression signature, and 3) gauging chemical concentration and dose response based on changes in expression patterns. We will test the response of the arrays to the EPA's 12 persistent bio-accumulative toxins (PBT?s). If this work proves feasibility, Phase II will involve developing a reasonably comprehensive Pimephales array as well as beginning arrays for Daphnia, duckweed, and green algae.